Preparation of active alumina agglomerates of high-mechanical strength

ABSTRACT

The preparation of active alumina agglomerates of highmechanical strength and low-active surface consisting of treating pellets of alumina in an autoclave in an acidic medium at a temperature above 100* to 250* C. for a time within the range of 1-20 hours, followed by drying the treated pellets and calcining the dried pellets at elevated temperature.

Unite States atent Continuation-impart of application Ser. No. 562,076,.Iuly l, 1966, now Patent No. 3,480,389. This application Nov. 21, 1969, Ser. No. 878,882

The portion of the term of the patent subsequent to Nov. 25, 1986, has been disclaimed.

[54] PREPARATION OF ACTIVE ALUMTNA AGGLOMIERATES 0F HIGH-MECHANICAL STRENGTH 3 Claims, No Drawings [52] US. Cl 23/143, 23/14 I, 252/463 [51] Int. Cl COH7/02, BOl j 1 H58 [50] Field of Search 252/463.6; 23/143 [56] References Cited UNITED STATES PATENTS 2,774,744 [2/1956 Barrett 23/143 X 3,480,389 11/1969 Graulier 23/l43 Primary Examiner-M. Weissman Allorney-McDougall, Hersh & Scott ABSTRACT: The preparation of active alumina agglomerates of high-mechanical strength and low-active surface consisting of treating pellets of alumina in an autoclave in an acidic medium at a temperature above l00 to 250 C. for a time within the range of l-20 hours, followed by drying the treated pellets and calcining the dried pellets at elevated temperature.

PREPARATION OF ACTIVE ALUMINA AGGLOMERATES F HIGH-MECHANICAL STRENGTH This is a continuation-in-part of my copending application Ser. No. 562,076, filed July 1, 1966, and entitled Active Alumina Agglomerates of High-Mechanical Strength and Method" now US. Pat. No. 3,480,389.

This invention relates to agglomerates of active alumina characterized by high-mechanical strength and relatively small active surface and it relates more particularly to agglomerates of the type described which find use as catalyst carriers and to the method for the preparation of same.

it is known that heterogeneous catalysis necessitates the use of catalyst carriers having different specific surfaces, depending somewhat upon the reactions to be carried out. The agglomerates of active alumina, which are often used as catalyst carriers, can be obtained in various forms such as granules, extruded products, chiefly from alumina trihydrate of the hydrargillite variety, partially and rapidly dehydrated and which can thereafter be set in the presence of water or a moist atmosphere. The regulation of the active surface of such agglomerates is obtained by varying the calcination temperature following agglomeration in which calcination is employed to reactivate the agglomerates. For obtaining large active surfaces, the reactivation temperature is lower than 1000 C. and agglomerates are secured under such conditions having good mechanical strength. However, in other cases, where the agglomerates must have a smaller surface area, this is obtained by calcination for reactivation at temperatures which are somewhat inversely proportional to the active surface.

it is noted that the mechanical strength of the agglomerates depends greatly on the reactivation temperature. Mechanical strength or solidity is good for calcination carried out at relatively high temperatures such as 1400 or 1600 C. in which the resulting active surface is very small, such as of the order of one M. /g., while the solidity of the agglomerates calcined at temperatures in the order of l000 C, is less satisfactory. The specific surface of the latter is larger, such as about m. /g., and it is suitable for different reactions.

in order to overcome this loss in mechanical strength, it has been proposed to make use of different solutions. In the French Pat. No. 1,386,364, filed on Dec. 2, 1963, description is made of the preparation of activated alumina by treatment ofthe alumina in an autoclave in the presence of water and the reactivation thereof by calcination at various temperatures. According to this method, reactivated agglomerates having improved mechanical strength are obtained at temperatures ranging from 800/l000 C. to 1400/1600 C. the mechanical strength being evaluated by reference to the crushing strength. It is believed that this increase in mechanical strength for surfaces of 10 m.-/g. is due to a difference in the way of the evolution of the crystalline structure as a function of reactivation temperature.

Though the solidity of the products thus obtained is satisfactory and permits use in industrial practice, applicant has found a process for the preparation of agglomerates of alumina, the active surface of which is capable of being regulated within large limits and which enjoys high-mechanical strength, even greater than the strengths produced in accordance with the process of the aforementioned French patent. This new process consists in treating active alumina agglomerates in an acidified aqueous medium in an autoclave at a temperature greater than 100 C. and preferably at a temperature within the range of 150 to 250 C. for a period of time ranging from 1 to hours. The treated agglomerates are dried and calcined at temperatures depending upon the desired specific surface and it is an object of this invention to produce and to provide a method for producing high-strength activated alumina agglomerates of the type described having different specific surfaces including low-surface areas.

Treatment of the alumina agglomerates in an autoclave, under acidic conditions, is believed to bring about the transformation of the alumina to boehmite, as shown by X-ray diffraction. However, the reason for the large increase in mechanical strength of the agglomeratesis not well known. It

may be that the texture of the boehmite crystals obtained is different and provides a better cohesion between dehydrated and reactivated crystals.

In accordance with the practice of this invention, it is possible to treat different alumina agglomerates in the autoclave to embody different ways of achieving the acid influence. For example, prior to their treatment in the autoclave, the agglomerates can be impregnated with the acid either in vapor phase or in liquid phase. 1t is also possible to treat the agglomerates without previous impregnation with the acid. In such event, the acidity is provided by an aqueous liquid in the autoclave. AS the acid, use can be made of any acid, their effects being sensibly the same. However, it is preferred to make use of certain acids depending upon their volatility.

The following examples, which are given by way of illustration, but not by way of limitation, concern the vapor phase treatment in an autoclave of pellets of active alumina in which the pellets have previously been impregnated either with acetic acid or nitric acid. The values given in the table relate to the total porous volume, the percent loss by attrition with microcrushers under conditions which can be compared, and the average crushing strength of the pellets for different temperatures of thermal treatment. For comparison, the results are given of the values secured with pellets which have not been treated in an autoclave but have otherwise been calcined at elevated temperature, and with pellets which have been treated in an autoclave but in the presence of water and calcined.

EXAMPLE 1 Pellets from 2 to 5 mm. in diameter are prepared by agglomeration of alumina having a large active surface and which have been moistened with water. These pellets, after drying, are'impregnated with 2 percent by weight acetic acid based upon an alumina content calculated as A1 0 The impregnated pellets are treated in an autoclave filled with steam at a temperature of 215 C. for 15 hours. After drying at 1 10 C., separate batches were calcined at temperatures of 1000", 1 and 1200 C.

EXAMPLE 2 Pellets prepared in accordance with the preceding example 1 are impregnated with 5 percent acetic acid based upon the weight of the alumina and treated in the autoclave, dried and reactivated under the same conditions as in example 1.

EXAMPLE 3 Under the same general conditions as those of the preceding examples 1 and 2, pellets of alumina are impregnated with 15 percent by weight acetic acid based upon the alumina. The calcination, after drying, is carried out at 500, 900, ll00 and 1200 C.

EXAMPLE 4 Under the same general conditions as those of the preceding examples, the same type of pellets are impregnated with 15 percent nitric acid based upon the alumina. After drying, the treated pellets are calcined at temperatures of 500, 1 100 and 1200 C.

1 It) 45 54 H 3 Sill) l3) 5 7 6.2

Example 3 900 65 4 S 7.5

[.HlU 49 0.66 65 93 LZUU H 0.53 6 8 I0 Example 4 500 I54 m5 l, l (Ill 45 H Pellets not 500 350 0.63 3 llJ treated "I l,l(lll 97 0.63 13 iiiitocliitc IJIH] [4 A $0 2 Pellets ll!) 25 50 l 5 treated in MN! 57 0.63 24 tluti clati: ljlllil J0 Z" J 7 I, l Oil l2 6 0 L200 9 0.55 H N 2 From the foregoing date it will be seen that pellets which have not been treated in an autoclave and which are reactivated at a temperature of 500 C. give large surface areas (350) and high solidity (3 percent) by comparison with the same pellets reactivated at higher temperature in which the surface area is 97 (at 1100 C.) and 14 (at l200 C.) and in which the loss by attrition is 18 percent (at 1 100 C.) and 30 percent (at l200 C.) On the other hand, when the pellets are treated in an autoclave in the presence of an acid, in accordance with the practice of this invention, these same pellets have a desirable small surface area at the same temperature of reactivation and with increased mechanical strength as evidenced by the reduction in loss by attrition. Pellets treated in an autoclave in an aqueous medium and in the absence of acid gave intermediate results but, in any event, poorer than those obtained by acid treatment in an autoclave in ac cordance with the practice of this invention.

Other acids that may be used may be represented by such inorganic acids as hydrochloric acid, sulfuric acid, phosphoric acid, hydrobromic acid and the like, or such organic acids as formic acid, acetic acid. propionic acid and halogenated derivatives thereofsuch as trichloroacetic acid, dichloroacetic acid, trichloropropionic acid, tribromoacetic acid and the like, as represented by the following additional examples:

EXAMPLES 5-8 Pellets in accordance with example 1 were impregnated with various acids listed in the following tabulation in amounts whereby the alumina retained 5 percent by weight of the acid. The pellets were treated for hours in an autoclave at a pressure of bars, corresponding to a temperature of about 210 C. A small separate water tank was placed in the autoclave during the period of treatment.

The different samples were dried at a temperature of 1 10 C. in an oven and then calcined for 4 hours at different temperatures, as set forth in the following tabulation. The control was processed in the same manner,

In the following table, the specific surface is set forth in LII square meters (m /g), the total porous volume in cc./gram, the loss by attrition in percent of the initial weight, and the average resistance to crushing in kg. of the balls treated.

Drying Total Loss Resist Tcmpcraturc Specific porous by ance to or Surface volume atiri- Crushing Calcinalion tion ltxilmplcfi H0 3| 1) 42 l'itlmlL' Acid Lilli) l8 2 9 9 3 l' xiimplch I10 67 0 42 lrlchlfiftl hlltl 9B 0 54 0 9 ll 7 acetic acid H00 65 0 52 I K H l l,|(l(l IS '4 Z 7 3 [.xavnplc7 I10 59 0.42 4 7 Hydrochloric hilt) I08 0 53 l 5 ll 7 acid Kilt) 75 (l 53 2 l0 l l01) 9.] 3! H16 Example? Ill) 63 7 l sulfuric 600 I48 0 2 l3 8 Acid H00 0 7 l4 5 l. l ()0 2| 2 6 l0 4 Control ll() 29 0.42

flutocluvcd 601) 55 0 54 4 4.3 in water 300 40 O 54 J 7 4 3 l ltlt) l4 5 3 3 6 2 Untreated 500 340 0.52 ll l Control l.|(lt) 80 16 J 5 it will be understood that various changes may be made in the process without departing from the spirit of the invention. For instance, it is often times advantageous to calcine the ag glomerates at temperatures below l000 C. and particularly in the order of 500 C. prior to treatment by the acid and to their treatment in the autoclave.

l claim:

1. A process for the preparation of active alumina ag glomerates of high-mechanical strength and predetermined active surface constituting of the steps of treating pellets of alumina in an autoclave in the presence of steam in an acidic medium wherein the acid is selected from the group consisting of hydrochloric acid, sulfuric acid, phosphoric acid, hydrobromic acid, formic acid, chlorinated and brominated derivatives of acetic acid, propionic acid and chlorinated and brominated derivatives thereof at a temperature from C. to 250 C. for a time within the range of 1-20 hours, drying the treated pellets and calcining the dried pellets at an elevated temperature.

2. The process as claimed in claim 1 in which the pellets are acidified by impregnating the pellets with the acid before treatment in the autoclave.

3. The process as claimed in claim I in which the pellets are acidified by treatment with an acid while in the autoclave.

' x UNITED "ST-ATEfi-PA'EEN?OFFICE I CERTEHCATE CD'RRECTEON PatentNo. 3,629,914 Dated December 21, .1971' lm',ent or(s) Maxime Gr'aulier I I v It is certifiedthaterror appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

hCo'l'umn 3,- line 11, under the numeral "415'" I i p;-'.insert fthe fnumeral "ll" the following sub-headings in the five columns: C m C/Q kg Column 4, in the tabulation under Example 5,

insert the following in the second and third' lines of the five columns:

Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD MQFLEI'CHER ,JRQ ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 6O376-P69 u.sv GOVERNMENT PRINTING OFFICE: 1969 (1-366-334 FORM PO-105O (10-69) 

2. The process as claimed in claim 1 in which the pellets are acidified by impregnating the pellets with the acid before treatment in the autoclave.
 3. The process as claimed in claim 1 in which the pellets are acidified by treatment with an acid while in the autoclave. 